Process for preparing 4-phenyl-1, 2-dithiole-3-thione



States P tent 11]., assignor toStandard Oil Company, .Chicago,

111., a corporation of Indiana No Drawing. Application-=March 26,1956 Serial No. 573,588

" Claims. ]((:I. 260-327) This invention relates to the preparation of phenyl trithione from alpha methyl styrene-by reaction with sul-. .fur. ,of my pending application's. N. 433,788, filedflune 1, 1954, nowabandoned.

The present application is a continuationrin part The preparation "of trithioneslbysulfurization of olefinic materials, including styrenes, is known. The known.

reaction however-is large ly of theoretical interest-because of low yields of trithione' and the-'diificult problem of purification presented in separating the pure trithione from the reaction mixture. Also, the reaction must be run in a bomb or pressure type apparatus at super-atmospheric pressure since the reaction goes at temperatures only above 200 C.

I have discovered that excellent yields of 2-phenyl trithione (4-phenyl-1,2-dithiole-3-thione) can be obtained from alpha-methyl styrene by a catalytic reaction conducted in a particular manner. According to my invention, the alpha-methyl styrene is gradually added to a reaction mixture comprising sulfur, an inert organic solvent and a small amount of a strong, hydrocarbon soluble organic base, more particularly a diaryl guanidine such as di-o-tolyl guanidine. The reaction mixtures is maintained at a temperature in the range of about 140 to 200 C., preferably 150 to 165 C. After completion of reaction, the reaction mixture is cooled and the trithione product is separated from the reaction solution as a crystalline product.

In the reaction, the structural configuration of alphamethyl styrene appears to be important in obtaining the high yields of the catalytic reaction of the invention since the reaction goes less well with other alkenyl aromatics. Di-o-tolyl guanidine has particular value as a catalyst for promoting the desired reaction. Other aryl guanidines such as diphenyl guanidine have valve, giving approxinmately equivalent reaction rates, but the yields of trithione product with di-o-tolyl guanidine in general run significantly higher. Other hydrocarbon soluble, strong organic bases such as aliphatic amines may be used. Secondary and tertiary butyl amines are examples of useful liquid aliphatic amines providing reaction rates substantiallly equivalent to that of the guanidines. The catalysts are used in small concentrations, usually in the range of about 0.01 to 2% by weight, preferably about 0.2% by weight.

The process is further characterized by the addition of the alpha-methyl styrene feed gradually to sulfur in an inert organic reaction medium. I have found that when the reaction is conducted in ordinary fashion by admixture of the reactants, yields are low and the rate is very slow. The use of a large excess of sulfur helps promote the reaction but complicates the product separation and purification problem. Advantageously, an excess of alpha-methyl styrene to sulfur is used in the invention. The ratio may vary from about 1 mole of feed per gramatom of sulfur to 1 mole per 5 gram-atoms of sulfur. I

prefer to use a ratio in the range of 1 mole:l:5 gram- 7 atoms to 1 mole:2.25 gram-atoms. The reaction is conducted at a temperature in th'e range of about 140 up to 200 C.'preferably'atabout150 165 C.'-andtl1e "the additiondf feed -is continued "at a rate" maintaining reaction until thesulfur'in the reaction zone *is consumed, usua1ly-abouf4 to 40' hoursfor" batch operation.

The reaction medium may comprise any organic sol- "vent which is sufii'ciently inert underthereabtiomconditions, i. eLdoes not react-withsulfur to an'extent interfer- "in'g' withyield and/or?producfqu'ality. The solvent also ""should be sufiiciently hl'gh boiling to permit reaction in therange "of1-50 to' 165 Crwithout resorting to the use of elevatedpressure. A tertiary=alkyl -benzene"such=as t-butyl benzene is "particularlysuitable. *Itdoebsnot react with sulfur under-fthe reaction coriditionsfover a long period of time, "and it-has a" sufficiently low boilingpoint to permiteasyrecoveryby"distillationj 0ther't-'alkyl benzenes such as t-amyl and t-hexyl benzene alsomay be used. Lighter aromatics such as benzene are low boiling andreq'uire "the use o'fpre ssurebut otherwiseare suitable. 'Alipllatic'hyd'rocarbons tendtomeact over an extended re- "actio'n period,lowering 'the purity of the trithione product or resulting in higher! consumption of 'solvent, and thus a'dd to'tlie'cost 'of the process. '-The normal'paraffins such as n-octane or n-decane are least objectionable from this standpoint.

A particular advantage of the process, in addition to high yields of the order of to is the convenience in separation and purification. Product recovery may be accomplished simply by cooling the reaction mixture and filtering or otherwise separating the crystalline trithione product. The mother liquor then can be distilled at reduced pressure or in the presence of steam to recover the solvent and any unreacted feed. The recovered solvent and/ or unreacted feed can be recycled. Additional trithiones may be recovered from the reaction mother liquor by partial evaporation followed by cooling and filtering. The process is susceptible of continuous operation with recycle. By contrast, the procedure of Bottcher and Luttringhaus (Ann. 557, 89, 1947) using a mixture of sulfur and olefinic feed results in unreacted sulfur and requires costly chemical separation techniques as through formation of a mercuric chloride adduct to recover a pure product.

The following examples are illustrative of the operation of the invention and of the advantages obtainable compared to more conventional means for conducting the reaction (compare Example I with Examples II and III).

Example I To a solution of 19.2 grams (0.6 gram atom) sulfur and 0.394 gram di-o-tolyl guanidine in ml. t-butyl benzene was added 47.2 grams (0.4 mole) wrnethyl styrene dropwise over 8 hours. The red solution was kept at 1560 C. for 16 hours, then cooled to 5 C. There crystallized 17.9 grams, 70%, 4-phenyl-1,2-dithiole-3-thione, M. P. -121" C. Anal. calcd. for C H S C, 51.42; H, 2.86; S, 45.72; mol. wt. 210. Found: C, 51.30; H, 3.00; S, 45.90; mol. wt. 209. The trithione filtrate gave, on distillation, 128 ml. (112 grams) of colorless distillate boiling at 110-135" C. at mm., of which 82 gram is the original t-butyl benzene and 30 gram is a-methyl styrene. The residue weighed 9 grams.

Example 11 A mixture of 129.3 ml. (1 mole) a-methyl styrene and 48 grams (1.5 gram-atoms) sulfur was heated at 156 C. After 144 hours the presence of free sulfur was tested by means of the ASTM copper strip corrosion test and the strip was still 10. The solution was cooled, precipitating 27 grams of sulfur, but no trithione. Distillation gave 119 cc. unreacted a-methyl styrene.

Example 111 A mixture of 129.3 ml. (1 mole) a-methyl styrene 96 grams (3 gram-atoms) sulfur and 1.8 grams (0.6%) di-o-tolyl guanidine was heated at 156 C.- After 1 8 hours the copper strip had dropped from 10 to 7. The mixture was cooled to 5 0., giving 32 grams based on sulfur) 4-phenyl-1,2-dithiole-3-thione, M. P. 120 C.

The filtrate was distilled in vacuo, giving ml. a-methyl of trithione was obtained, and 82% of the original.

alpha-methyl styrene unconverted to trithione was recovered.

1. A process for preparing 2-phenyl trithione (4- phenyl-l,2-diothiole-3-thione) which comprises adding alpha-methyl styrene gradually to a reaction medium comprising sulfur and an inert organic solvent, conducting the reaction at a temperature in the range of about to 200' C. in the presence of a catalytic amount of a strong, hydrocarbon soluble organic base, cooling the mixture after completion of reaction and separating crystallized trithione from the reaction liquor.

2. The process of claim 1 in which the temperature is maintained in the range of about to C.

3. The process of claim 1 in which solvent and unreacted feed are recovered from the reaction liquor by distillation for recycle.

4. The process of claim 1 in which the catalyst is an aryl guanidine.

5. The process of claim 1 in which the catalyst is di-ortho-tolyl guanidine.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain May 18, 1955 OTHER REFERENCES Boettcher: Annalen, 557: 89-407 (1947). MacArdle: Use of Solvents, pages 1-20, 114-128.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORBECTIN Patent Non 2,857,399 October 21, 1958 Ellis KIu Fields It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

Column 1, line 49, for "valve" read value lines 49 and 50, for "approximately" read approximately lines 55 and 56, for "substantiallly" read substantially line '71, for "l molezlz5" read 1 molezlo5 column 2, line 39, for "557" read me 557 column 3, line 2, for "1293 ml (1 mole)" read M 258.6 mle (2 moles) o Signed and sealed this 27th day of January 1959a i SEAL) T ttest:

tom AXLTNE ROBERT c. WATSON Attesting Oflicer Commissioner of Patents 

1. A PROCESS FOR PREPARING 2-PHENYL TRITHIONE (4PHENYL-1,2-DIOTHIOLE-3-THIONE) WHICH COMPRISES ADDING ALPHA-METHYL STYRENE GRADUALLY TO A REACTION MEDIUM COMPRISING SULFUR AND AN INERT ORGANIC SOLVENT, CONDUCTING THE REACTION AT A TEMPERATURE IN THE RANGE OF ABOUT 140* TO 200*C. IN THE PRESENCE OF A CATALYTIC AMOUNT OF A STRONG, HYDROCARBON SOLUBLE ORGANIC BASE, COOLING THE MIXTURE AFTER COMPLETION OF REACTION AND SEPARATING CRYSTALLIZED TRITHIONE FROM THE REACTION LIQUOR. 